The present invention relates to a steering apparatus for an electric industrial vehicle, and more particularly to a steering apparatus for an electric industrial vehicle having a fully hydraulic power steering system.
For example, an electric counterbalanced forklift disclosed in U.S. Pat. No. 5,542,490 has a pair of drive wheels that are driven by an electric motor, a pair of steered wheels, and a steering angle sensor for detecting the steering angle of a steering wheel. Based on the steering angle, a controller determines a steering speed of the steering wheel, and controls a hydraulic pressure control motor to operate at a rotational speed that corresponds to the steering speed. As a result, a hydraulic pump supplies working fluid at a rate corresponding to the steering speed to a steering control valve.
In the case of a steering apparatus disclosed in Japanese Laid-Open Patent Publication No. 11-235982, a controller determines an angular velocity of a steering wheel based on the angle of the steering wheel, which angular velocity is detected by a steering wheel angle sensor, and controls a motor to supply working fluid to a hydraulic pump at a rate corresponding to the angular velocity.
Generally, on electric forklifts, the steering angle of a steering wheel is detected, and the rotational speeds of right and left drive motors are controlled based on the steering angle. The forklift is smoothly turned based on the difference developed between the rotational speeds of the propulsive motors corresponding to the steering angle.
As described above, if the hydraulic pump is to be controlled based on the steering speed of the steering wheel when the steering wheel is turned, a detector needs to be newly installed for detecting the steering speed of the steering wheel. As a result, the number of parts of the steering apparatus and the number of assembling steps for the steering apparatus are increased.